The present invention relates to an automatic contact-pin setting apparatus for testing off-grid printed circuits.
As is known, the so-called "in-grid" printed circuits, i.e. printed circuits supported on a plate formed with a plurality of test through holes arranged at a standard pitch, are test checked using a suitable control unit including a bed of needle-like metal plugs (feelers) and a processor to which the feelers are connected. The metal plugs are set in a plate of plastics material formed with a large number of perforations or holes which are arranged in a regular grid (normally with a hole pitch of 2.54 mm) and in which the feelers are accommodated.
In the instance of the printed circuit being provided with irregularly arranged checking locations, instead of the cited grid (i.e., the circuit is an "off-grid" printed circuit), it becomes necessary, in order to carry out the test check, to use a suitable adaptor (i.e., an adaptor for "off-grid" printed circuits) which can provide a pattern of the feelers on the check bed exactly matching the pattern of the check locations on the printed circuit to be tested. Such an adaptor was developed by the Applicant of this application and essentially comprises a top reference plate of plastics material formed with bores or holes arranged "off-grid" according to the printed circuit pattern to be tested, and a lower basic plate or plug bed arranged underneath the "off-grid" plate and having metal plugs accommodated in it according to a regular grid arrangement and in electric contact with a suitable scanning apparatus.
Metal contact-pins are manually inserted downwardly into the holes provided in the upper "off-grid" plate so that each of them extends to the nearest hole in the lower regular grid basic plate to contact the plug or feeler in it. The connecting pins also project upwardly into a respective hole in a printed circuit to be tested overlying the upper plate.
As mentioned above, it is current practice to have the contact-pins insertion carried out manually by an operator, which is time-consuming on account of the large number of pins involved. An additional disadvantage of such a conventional technique is that the operator, after inserting a contact-pin through a hole in the top plate, is unable to randomly insert the pin bottom portion through one of the lower plate holes (normally four in number) directly underlying the hole in question where plugs or feelers are located. The selection of one of the underlying holes made by the operator does not always lead, therefore, to the achievement of an optimum pin setting. More particularly, this situation results in technical difficulties both as regards physical positioning of each contact-pin owing to relatively large inclination of the contact-pin from the normal to the adaptor plane with attendant less-than-optimum connection to a corresponding feeler located underneath in the plug bed (lower plate), and its optimum functional positioning determined by the hole selected on the lower plate whose feelers are designed to establish electric connection for testing the printed circuit placed on the top plate. From the economical standpoint, manual insertion of the contact-pins, by requiring long operation times, cannot permit reuse of the contact-pins for different circuit patterns. In other words, large contact-pin stocks for various printed circuit types must be maintained, since it would be uneconomical to disassemble, and consequently destroy an already formed pattern, contact-pins previously placed on an adaptor intended for a specific circuit. Moreover, as an added disadvantage, manual application of the contact-pins disallows full repeatability of the positioning of the same, if required.